Valve operating device for internal combustion engine

Abstract: A valve operating device for an internal combustion engine includes a plurality of rocker arms, a plurality of cams provided on a cam shaft in independent correspondence to the rocker arms, and a connection switchover device capable of switching over the connection and disconnection of the rocker arms in combination. In this valve operating device, the connection switchover device includes a switchover piston slidably fitted into the first rocker arm operatively connected to an engine valve with one end facing a hydraulic pressure chamber, a switchover pin slidably fitted into the second rocker arm adjacent the first rocker arm with one end abutting against the other end of the switchover piston, a limiting member which is slidably fitted into the third rocker arm operatively connected to another engine valve and adjoining the second rocker arm on the opposite side from the first rocker arm and which abuts against the other end of the switchover pin, and a spring biasing mechanism provided in the third rocker arm for biasing the limiting member toward the hydraulic pressure chamber by a spring force which enables the sliding stroke of each of the switchover piston, the switchover pin and the limiting member to be changed at two stages in response to increasing of the hydraulic pressure in the hydraulic pressure chamber at two stages. The switchover pin has an axial length such that in a condition in which an axial one end thereof has been fitted into one of the first and second rocker arms, the other end thereof is located between the other of the first and third rocker arms and the second rocker arm.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a valve operating device for an internal combustion engine, which is capable of changing the operating characteristics of engine valves, according to the preamble of claim 1. DESCRIPTION OF THE PRIOR ART A valve operating device for an internal combustion engine has already been known, for example, from Japanese Patent Application Laid-open No.100210/88, which includes a plurality of rocker arms disposed adjacent one another for swinging movement about a common axis, a plurality of cams provided on a cam shaft in independent correspondence to the rocker arms, and a connection switchover means capable of switching over the connection and disconnection of a combination of the rocker arms. In the connection switchover means of such valve operating device, a hydraulic pressure is applied to a hydraulic pressure chamber from an axial one direction of switchover members slidably fitted in the rocker arms and connected to one another, and the spring characteristic of a return spring acting in the axial other direction of the switchover members is changed at a plurality of stages in order to enable the sliding stroke of each switchover member to be switched over at a plurality of stages by switching over the hydraulic pressure applied to the hydraulic pressure chamber at a plurality of stages. However, in order to enable the connection and disconnection of the adjacent rocker arms to be switched over at each of the sliding strokes of the switchover members, each of the switchover members must be formed into a stepped configuration, resulting in a troublesome machining. Moreover, in the prior art device, the rocker arms are not in their connected states in a condition in which each of the switchover members has not been slid. Therefore, if a free rocker arm capable of being freed relative to the engine valves is disposed between a pair of driving rocker arms operatively connected to the engine valves and corresponding to cams for substantially stopping the engine valves, when the connection switchover means has been brought into its inoperative state due to any cause in an operating range in which the engine valves should be driven by the free rocker arm, the free rocker arm cannot be connected to any of the driving rocker arms, and when the cams corresponding to the driving rocker arms are arranged to substantially stop the engine valves, the engine valves are also brought into their substantially stopped states. In the above prior art device, all the switchover means are simultaneously operated in a switching manner and hence, the degree of freedom of the connection and disconnection of the rocker arms in combination is limited. In order to change the operating characteristics of the engine valves variously, it is desirable to increase the degree of freedom of the connection and disconnection of the rocker arms in combination. A valve operating device for an internal combustion engine has already been also known, for example, from Japanese Patent Publication No.75729/91, which includes a driving rocker arm operatively connected to an engine valve, first and second free rocker arms adjacently disposed on opposite sides of the driving rocker arm, so that they can be freed relative to the engine valve, first and second cams provided on a cam shaft in independent correspondence to the free rocker arms and having cam profiles intersecting each other, and connection switchover means capable of switching over the connection and disconnection of the driving rocker arm to and from the free rocker arms. In this device, the engine valve is opened and closed relatively slowly in a high-speed operating range of the engine to insure a sufficient opening area desired by the engine, and the engine valve is opened and closed relatively rapidly in a low-speed operating range of the engine to insure a sufficient opening area desired by the engine, by switching over a state in which the first free rocker arm is connected to the driving rocker arm operatively connected to the engine valve to open and close the engine valve by the first cam and a state in which the second free rocker arm is connected to the driving rocker arm operatively connected to the engine valve to open and close the engine valve by the second cam. However, in switching over the state in which the driving rocker arm is connected to the first free rocker arm and the state in which the driving rocker arm is connected to the second free rocker arm, the switching operation should be completed at one timing when the first and second rocker arms have been stopped by base circle portions of the first and second cams. However, when both the connection switchover means have been brought into their connecting states at a displaced timing of switching, an abnormal behavior such as a valve jumping may be produced in the engine valve due to the intersection of the profiles of the first and second cams for swinging the first and second free rocker arms. Further, a valve operating device for an internal combustion engine has already been known, for example, from Japanese Patent Publication No.75729/91, which includes a rocker arm swingably carried on a rocker arm shaft and having a support sleeve integrally provided thereon with its inner surface put into sliding contact with an outer surface of the rocker arm shaft, another rocker arm swingably carried on the support sleeve, an engine valve operatively connected to at least one of the rocker arms, and a connection switchover means provided between the support sleeve and the other rocker arm and capable of switching the connection and disconnection of the rocker arms from one to another in response to the switching operation of a switchover piston having an axis perpendicular to an axis of the rocker arm shaft. In such valve operating device, the switchover piston having the axis perpendicular to the axis of the rocker arm shaft is fitted into the support sleeve for sliding movement between a connecting position in which it is in engagement with the rocker arm carried on the support sleeve and the engagement with the rocker arm is released. For this reason, the support sleeve must be increased in size and correspondingly, the rocker arm swingably carried on the support sleeve is also increased in size, resulting in an increased inertial moment. When the rocker arm is being swung in the disconnecting state, a centrifugal force is applied to the switchover piston outwardly in a radial direction of the rocker arm shaft and hence, when the spring force of a return spring for biasing the switchover piston toward a disconnecting position is small, a tip end of the switchover piston is urged against an inner surface of the rocker arm by such centrifugal force, resulting in an increased wear between the switchover piston and the support sleeve. If the spring force of the return spring is increased, the hydraulic pressure force applied to the switchover piston during connection must be increased. In a high-speed rotational range, it is difficult to overcome the wear problem even by the increase in spring force of the return spring. A connection switchover means having an operating axis perpendicular to an axis of the rocker arm shaft is disclosed in Japanese Patent Application Laid-open No. 72403/92. In this connection switchover means, a pair of rocker arms are adjacently disposed on opposite sides of a rocker arm integral with a rocker arm shaft to abut against cams having different profiles, and connection switchover means provided between the rocker arm shaft and the rocker arms disposed on the opposite sides, respectively. In this connection switchover means, a problem of an increase in size of the rocker arms and a problem of a wear are not arisen, but a combination of the rocker arm integral with the rocker arm shaft and the rocker arms disposed on the opposite sides of such rocker arm is disposed for every cylinder and hence, in a multi-cylinder internal combustion engine, hydraulic pressure circuits leading to oil passage provided in the rocker arm shafts in cylinders must be provided in a cylinder head, resulting in a complicated arrangement of the hydraulic pressure circuits in the cylinder head. In the generic embodiment of GB 2 199 079 A, Figs. 7, 8, the hydraulic switchover piston/switchover pin/limiting mechanism is operated by one single hydraulic pressure. In another embodient shown in Fig. 12 thereof, separate switchover means for two rocker arms on opposite sides of three mutually adjacent rocker arms are operated sequentially by a two stage increase of the hydraulic pressure. The EP-A-0 546 820 shows an arrangement, wherein in all operational ranges of the engine the switchover pin interconnects at least two of the three rocker arms. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to insure a state in which at least one of rocker arms connected to engine valves is connected to a further rocker arm located between these rocker arms, in addition to the simplification of the switchover member. It is a further object of the present invention to increase the degree of freedom of connection and disconnection of the rocker arms in combination. To achieve the first object, according the present invention, there is provided a valve operating device for an internal combustion engine, comprising: a plurality of rocker arms including at least first, second and third rocker arms adjacently disposed for swinging movement about a common axis; a plurality of cams provided on a cam shaft in independent correspondence to said rocker arms ; and a connection switchover means capable of switching over between a connection and disconnection of said rocker arms in various combinations, wherein said connection switchover means includes: a switchover piston slidably fitted into said first rocker arm operatively connected to an engine valve and having one end facing a hydraulic pressure chamber ; a switchover pin slidably fitted intro said second rocker arm adjacent said first rocker arm , and having one end abutting against the other end of said switchover piston ; a limiting mechanism which is slidably fitted into said third rocker arm operatively connected to another engine valve and adjoining said second rocker arm on an opposite side from said first rocker arm said limiting mechanism abutting against the other end of said switchover pin ; and a spring biasing mechanism (37) provided in said third rocker arm for biasing said limiting mechanism toward said switchover pin , said spring biasing mechanism enabling a sliding stroke of each of said switchover piston , said switchover pin (35) and said limiting mechanism to be changed at two stages in response to a two-stage increase in the hydraulic pressure in said hydraulic pressure chamber ; said switchover pin having an axial length such that when an axial one end of the switchover pin has been fitted into one of said first and third rocker arms, the other end of the switchover pin is located between the other of said first and third rocker arms and said second rocker arm, whereby at least two of the rocker arms including the second rocker arm are held in the connected state by said switchover pin in all operational ranges of the engine. With this feature of the present invention, it is possible not only to simplify the shape of the switchover pin to facilitate the machining thereof, but also to necessarily connect at least one of the first and third rocker arms operatively connected to the engine valve to the intermediate rocker arm. Therefore, even if the cams corresponding to the first and third rocker arms are arranged to substantially stop the engine valves, both the engine valves cannot be brought into their stopped state, irrespective of the operated state of the connection switchover means. With the above arrangement, it is ensured that at least one of first rocker arm, that is operatively connected to one engine valve, and third rocker arm, that is operatively connected to another engine valve, is held in a connected state with the intermediate second rocker arm. Thus, even when the second rocker arm is constructed so as to be associated with a high speed cam and to be associated with no engine valve, no lost motion means is required for this second rocker arm since it is always in connnection with the first or third rocker arm and thus can perform swinging motion with the aid of the first or third rocker arm. Preferably, said limiting mechanism comprises a first limiting member abutting against the other end of said switchover pin and a second limiting member , and wherein said spring biasing mechanism comprises a first spring interposed under compression between said first and second limiting members and and a second spring for urging said second limiting member toward said first limiting member , said first spring having a spring force set smaller than that of said second spring and acting on the first limiting member to separate the first limiting member from said second limiting member by a distance that corresponds to an amount of said switchover pin fitted into said first rocker arm when the other end of the switchover pin is located between the second and third rocker arms. Preferably the valve operating device for an internal combustion engine, comprises a plurality of rocker arms adjacently disposed for swinging movement about a common axis, a plurality of cams provided on a cam shaft in independent correspondence to the rocker arms, and a connection switchover means capable of switching over the connection and disconnection of the rocker arms in combination, wherein the connection switchover means includes a switchover piston fitted into one of the rocker arms on one side in a direction of adjacent arrangement of them with one end facing a hydraulic pressure chamber, a limiting member slidably fitted into one of the rocker arms on the other side in the direction of adjacent arrangement of them, a return spring for biasing the limiting member toward the one side in the direction of adjacent arrangement, and switchover pins fitted into intermediate two of the rocker arms in the direction of adjacent arrangement of them and disposed between the switchover piston and the limiting member, at least one of the switchover pins fitted into the intermediate rocker arms comprising a pair of pin members, and a spring interposed between the pin members for biasing the pin members away from each other by a spring force smaller than that of the return spring. With this feature, it is possible to increase the degree of freedom of the connection and disconnection of the rocker arms in combination, and to change the operating characteristics of the engine valves more variously by properly selecting the dispositions of the cams and the engine valves relative to the rocker arms. The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figs.1 to 3 illustrate an embodiment of the present invention, wherein Fig.1 is a vertical sectional side view of the embodiment, taken along a line 1-1 in Fig.2; Fig.2 is a plan view taken along a line 2-2 in Fig.1; and Fig.3 is a sectional view taken along a line 3-3 in Fig.1. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described by way of preferred embodiments with reference to the accompanying drawings. Figs.1 to 3 illustrate an embodiment of the present invention. Intake valves V I1 and V I2 as a pair of engine valves are provided in an engine body E and opened and closed by the actions of a stopping cam 22, a substantially stopping cam 23 and an operating cam 24 which are integrally provided on a cam shaft 21 driven at a rotational ratio of 1/2 synchronously with the rotation of an engine crankshaft, and first, second and third rocker arms 25, 26 and 27 which are disposed adjacently with one another for swinging movement about a common swinging axis parallel to the cam shaft 21. The cam shaft 21 is rotatably disposed at an upper portion of the engine body E and is integrally provided with the stopping cam 22, the substantially stopping cam 23 and the operating cam 24 in such a manner that the operating cam 24 is sandwiched between the stopping cam 22 and the substantially stopping cam 23. Thus, the stopping cam 22 has a profile which permits the intake valve V I2 to be closed and stopped, and is formed into a shape spaced at a constant distance apart from the axis of the cam shaft 21. The operating cam 24 has a base circle portion 24a having the same radius as the stopping cam 22, and a cam lobe 24b Protruding radially outwardly from the base circle portion 24a. The substantially stopping cam 23 has a profile permitting the intake valve V I1 to be substantially stopped and includes a base circle portion 23a corresponding to the base circle portion 24a of the operating cam 24, and a cam lobe 23b slightly protruding radially outwardly from the base circle portion 23a at a location corresponding to the cam lobe 24b of the operating cam 24. The first, second and third rocker arms 25, 26 and 27 are disposed adjacently to one another with the second rocker arm 26 being sandwiched between the first and third rocker arms 25 and 27, and are swingably carried on a common rocker arm shaft 28 which is rotatably carried on the engine body below the cam shaft 21. Moreover, the substantially stopping cam 23 is provided on the cam shaft 21 in correspondence to the first rocker arm 25; the operating cam 24 is provided on the cam shaft 21 in correspondence to the second rocker arm 26, and the stopping cam 22 is provided on the cam shaft 21 in correspondence to the third rocker arm 27. The first and third rocker arms 25 and 27 extend to positions above the pair of intake valves V I1 and V I2 , and tappet screws 29, 29 are advanceably and retreatably threadedly inserted into ends of the first and third rocker arms 25 and 27 and capable of abutting against upper ends of the intake valves V I1 and V I2 , respectively. A collar 30 is provided at an upper portion of each of the intake valves V I1 and V I2 , and valve springs 31 are interposed between the collars 30, 30 and the engine body E to surround the intake valves V I1 and V I2 , respectively, so that the intake valves V I1 and V I2 are biased in their closing directions, i.e., upwardly by the action of the valve springs 31. Further, the second rocker arm 26 is resiliently biased in a direction to contact with the operating cam 24 by a lost motion mechanism (not shown) Provided between the second rocker arm 26 itself and the engine body E. The connection and disconnection between the first, second and third rocker arms 25, 26 and 27 in combination are switched over by a connection switch-over means 32. The connection switchover means 32 includes a switchover piston 34 slidably connected to the first rocker arm 25 with one end facing a hydraulic pressure chamber 33, a switchover pin 35 slidably fitted into the second rocker arm 26 with one end abutting against the other end of the switchover piston 34, a limiting member 36 slidably fitted into the third rocker arm 27 to abut against the other end of the switchover pin 35, and a spring biasing mechanism 37 provided on the third rocker arm 27 for biasing the limiting member 36 toward the hydraulic Pressure chamber 33 by a spring force which enable the sliding stroke of each of the switchover pin 35 and the limiting member 36 to be changed at two stages. A bottomed guide hole 38 is provided in the first rocker arm 35 in parallel to the rocker arm shaft 28 and opens toward the second rocker arm 26, and the switchover Piston 34 is slidably fitted in the guide hole 38 to define the hydraulic pressure chamber 33 between the one end of the switchover piston 34 and a closed end of the guide hole 38. Moreover, the axial length of the switchover piston 34 is determined so that the other end of the switchover piston 34 is located at a position retracted from the position between the first and second rocker arms 25 and 26 toward pressure chamber 33 in a condition in which the switchover piston 34 has been slid to a position where the volume of the hydraulic pressure chamber 33 is minimized, as shown in Fig.3. A communication passage 39 is also provided in the first rocker arm 25 to communicate with the hydraulic pressure chamber 33, and an oil passage 40 (see Fig.1) is provided in the rocker arm shaft 28 to normally communicate with the communication passage 39 and thus with the hydraulic pressure chamber 33, irrespective of the swinging state of the first rocker arm 25. A guide bore 41 is provided in the second rocker arm 26 in parallel to the rocker arm shaft 28 and opens at opposite ends thereof in correspondence to the guide hole 38, and the column-shaped switchover pin 35 is slidably fitted in the guide bore 41. Moreover, the axial length L of the switchover pin 35 is determined so that its axial one end is fitted by a distance L 1 into the guide hole 38 in the first rocker arm 25, when the other end thereof is located at an intermediate position between the third and second rocker arms 27 and 26, as shown in Fig. 3. A small-diameter guide bore 42 opposed to the guide bore 41 and a large-diameter guide bore 43 are provided in the third rocker arm 27 in the named order from the side of the second rocker arm 26 and in parallel to the rocker arm shaft 28. The large-diameter guide bore 43 is coaxially connected to the small-diameter guide bore 42 through a step 44. The limiting member 36 formed into a bottomed cylinder-like configuration is slidably fitted into the small-diameter guide bore 42. The spring biasing mechanism 37 includes an auxiliary limiting member 45 formed into a bottomed cylinder-like shape and slidably fitted in the large-diameter guide bore 43 in the third rocker arm 27, a first return spring 46 mounted under compression between the limiting member 36 and the auxiliary limiting member 45, and a second return spring 48 mounted under compression between the auxiliary limiting member 45 and a stopping ring 47 fitted in the large-diameter guide bore 43 at a location near its outer end. The spring force of the second return spring 48 is set larger than the spring force of the first return spring 46. The limiting member 36 whose surface abutting against switchover pin 35 corresponds to the intermediate location between the second and third rocker arms 26 and 27 is spaced at a distance equal to the distance L 1 of fitting of the switchover pin 35 into the first rocker arm 25, apart from the auxiliary limiting member 45 which is in abutment against the step 44. The operation of the embodiment will be described below. In a condition in which the hydraulic pressure in the hydraulic pressure chamber 33 has been released, the switchover piston 34, the switchover pin 35 and the limiting member 36 are in their states in which they have been moved to the maximum toward the hydraulic pressure chamber 33 by the spring force exhibited by the spring biasing mechanism 37, with one end of the switchover pin 35 being received in the guide hole 38, and with the surface of the limiting member 36 abutting against the other end of the switchover pin 35 being located between the second and third rocker arms 26 and 27. Thus, the first and second rocker arms 25 and 26 are in their interconnected states in which one of the intake valves V I1 is opened and closed with a characteristic corresponding to the profile of the operating cam 24, while the second and third rocker arms 26 and 27 are in their disconnected states in which the other intake valve V I2 is brought into a closed and stopped state by the stopping cam 22. If a relatively low hydraulic pressure enough to overcome the spring force of the first return spring 46 of the spring biasing mechanism 37 is then applied to the hydraulic pressure chamber 33, the switchover piston 34 is moved by the distance L 1 by compressing the first return spring 46, until it causes the limiting member 36 to abut against the auxiliary limiting member 45 which is in abutment against the step 44. This causes the abutting surfaces of the one end of the switchover pin 35 and the switchover piston 34 to be located between the first and second rocker arms 25 and 26, and causes the other end of the switchover pin 35 to be received into the small-diameter guide hole 42. Thus, the first and second rocker arms 25 and 26 are brought into their disconnected states in which the one intake valve V I1 is brought into a substantially stopped state by the substantially stopping cam 23, while the other intake valve V I2 is opened and closed with a characteristic corresponding to the profile of the operating cam 24 in response to the connection of the second and third rocker arms 26 and 27. If a relatively high hydraulic pressure enough to overcome the spring forces of the first and second return springs 46 and 48 of the spring biasing mechanism 37 is further applied to the hydraulic pressure chamber 33, the switchover piston 34 is moved until it compresses the first return spring 46 to further force the limiting member 36 in abutment against the auxiliary limiting member 45 into the large-diameter guide bore 43, so that the other end of the switchover piston 34 is fitted into the guide bore 41 in the second rocker arm 26, and the switchover pin 35 is further forced into the small-diameter guide bore 42. Thus, all the first, second and third rocker arms 25, 26 and 27 are connected together, so that both the intake valves V I1 and V I2 are opened and closed with the characteristic corresponding to the operating cam 24. With such valve operating device, at least one of the first and third rocker arms 25 and 27 connected to the intake valves V I1 and V I2 holds its connection to the second rocker arm 26, and even if the connection switchover means 32 is inoperative for any reason, both the intake valves V I1 and V I2 cannot be brought into their substantially stopped states and into their stopped states. The switchover pin 35 may have a columnar simple shape and hence, is easy to machine. In the above-described embodiment, a stopping cam 22 may be used in place of the substantially stopping cam 23 and even in this case, a similar effect can be provided.

Claims: A valve operating device for an internal combustion engine, comprising: a plurality of rocker arms including at least first, second and third rocker arms (25, 26, 27) adjacently disposed for swinging movement about a common axis; a plurality of cams (23, 24, 22) provided on a cam shaft (21) in independent correspondence to said rocker arms (25, 26, 27); and a connection switchover means (32) capable of switching over between a connection and disconnection of said rocker arms in various combinations, wherein said connection switchover means (32) includes: a switchover piston (34) slidably fitted into said first rocker arm (25) operatively connected to an engine valve (V I1 ) and having one end facing a hydraulic pressure chamber (33); a switchover pin (35) slidably fitted into said second rocker arm (26) adjacent said first rocker arm (25), and having one end abutting against the other end of said switchover piston (34); a limiting mechanism (36, 45) which is slidably fitted into said third rocker arm (27) operatively connected to another engine valve (V I2 ) and adjoining said second rocker arm (26) on an opposite side from said first rocker arm (25), said limiting mechanism abutting against the other end of said switchover pin (35); and a spring biasing mechanism (37) provided in said third rocker arm (27) for biasing said limiting mechanism toward said switchover pin (35), characterized in that said spring biasing mechanism enabling a sliding stroke of each of said switchover piston (34), said switchover pin (35) and said limiting mechanism (36, 45) to be changed at two stages in response to a two-stage increase in the hydraulic pressure in said hydraulic pressure chamber (33); said switchover pin (35) having an axial length (L) such that when an axial one end of the switchover pin (35) has been fitted into one (25) of said first and third rocker arms, the other end of the switchover pin (35) is located between the other (27) of said first and third rocker arms and said second rocker arm (26), whereby at least two of the rocker arms including the second rocker arm (26) are held in the connected state by said switchover pin (35) in all operational ranges of the engine. A valve operating device according to claim 1, wherein said limiting mechanism comprises a first limiting member (36) abutting against the other end of said switchover pin (35) and a second limiting member (45), and wherein said spring biasing mechanism (37) comprises a first spring (46) interposed under compression between said first and second limiting members (36) and (45) and a second spring (48) for urging said second limiting member (45) toward said first limiting member (36), said first spring (46) having a spring force set smaller than that of said second spring (48) and acting on the first limiting member (36) to separate the first limiting member (36) from said second limiting member (45) by a distance (L 1 ) that corresponds to an amount (L 1 ) of said switchover pin (35) fitted into said first rocker arm (25) when the other end of the switchover pin (35) is located between the second and third rocker arms (26, 27).

Inventors: KONNO TSUNEO, KONNO, TSUNEO, KONNO, TSUNEO, C/O KABUSHIKI KAISHA
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1994
Main classification: F01L1
IPC codes: F01L1, F01L13